I am planning to fit 5x50w 12v SELV dowlights in my bathroom. The total amperage for this is going to be 20.83a - my question is does the high amps only occur AFTER the transformer, or do I need to consider this high current being drawn throughtout, right back from the consumer unit. ie do i need to upgrade theRCD and wiring to the bathroom?
SELV downlights
- Thread starter foxy10
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How did you make your calculations?
Welcome to the forum.
Your question leads me to think that you may not be in a position to carry out this work to the satisfaction of the local authority.
Electrical work in a bathroom is notifiable see
//www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law
You would be better getting a registered electrician to do this for you.
In direct answer to your question:
The secondary current of a transformer will only be the same as the primary current if the windings ratio is 1:1. Yours is not. You have a voltage ratio of about 20:1. (240volts > 12volts).
Can you work out what that will mean to the primary current?
Your question leads me to think that you may not be in a position to carry out this work to the satisfaction of the local authority.
Electrical work in a bathroom is notifiable see
//www.diynot.com/wiki/electrics:part_p:diy_electrical_work_and_the_law
You would be better getting a registered electrician to do this for you.
In direct answer to your question:
The secondary current of a transformer will only be the same as the primary current if the windings ratio is 1:1. Yours is not. You have a voltage ratio of about 20:1. (240volts > 12volts).
Can you work out what that will mean to the primary current?
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Thanks Taylor, as i mentioned, i'm PLANNING this, not actually doing it. Part of that is weighing up how much i need to replace, is it just the bathroom wiring, or the whole lot. I guess from your answer (with a question) that I need to replace the fuse and wire too.
and 5 x 50w = 250 / 230v = 1.086
Which is the current in the primary when 250 watts is passing across the transformer. Though add a bit for in-efficiency in the transformer. The wasted energy that makes the transformer get warm or hot.
250 watts of light in a bathroom ?
Under floor heating for the room above ?
Also chose the transformers for lamps carefully, make sure the transformers can take the load of the lamp or lamps.
Glad to hear that you are not doing it yourself!
As i said
So (in general terms) the primary current will be a 20th of the secondary current.
Your secondary current (you calculated correctly) as 20.833amps.
A 20th of that, as Bernard has stated is just over an amp, so your existing lighting circuit may be able to cope with that, depending on what it is already driving.
But your registered electrician can help you plan all that. I suggest you leave the supply of lights to him too.
There are a number of considerations: SELV may be required, they may have to be IP44, maybe better than that, depending on bathroom layout.
There's building regulations to comply with:
Among others, parts B, E, L and P will apply to downlights.
Then you/he will have to consider how you stop the heat from the room escaping into the loft. Do you have lots of insulation? Now you are going to make a swiss cheese out of your ceiling. You can't just put insulation over your downlights.
And all that steam, that will get drawn up into the loft space, and the moisture will rot your roof timbers - unless the lights are the right ones.
Oh yes, and lets not mention the fact that you will be burning 250watts to light a room that can be adequately lit with a 16watt low energy 2D light.
Still want to go ahead?
As i said
So (in general terms) the primary current will be a 20th of the secondary current.
Your secondary current (you calculated correctly) as 20.833amps.
A 20th of that, as Bernard has stated is just over an amp, so your existing lighting circuit may be able to cope with that, depending on what it is already driving.
But your registered electrician can help you plan all that. I suggest you leave the supply of lights to him too.
There are a number of considerations: SELV may be required, they may have to be IP44, maybe better than that, depending on bathroom layout.
There's building regulations to comply with:
Among others, parts B, E, L and P will apply to downlights.
Then you/he will have to consider how you stop the heat from the room escaping into the loft. Do you have lots of insulation? Now you are going to make a swiss cheese out of your ceiling. You can't just put insulation over your downlights.
And all that steam, that will get drawn up into the loft space, and the moisture will rot your roof timbers - unless the lights are the right ones.
Oh yes, and lets not mention the fact that you will be burning 250watts to light a room that can be adequately lit with a 16watt low energy 2D light.
Still want to go ahead?
Part C is often a consideration when you cut holes in a bathroom ceiling.
foxy - Google bathroom lighting - there are more non-recessed lights out there than you can shake a forest of sticks at, all of which:
a) will do a better job than 5 recessed torches
b) you can install yourself without it being notifiable
c) will be much quicker and easier to do than cutting all those holes and then having to build sealed enclosures around them in the loft.
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